The present invention relates to a solid bowl screw centrifuge having a rotating drum which surrounds a centrifuging chamber having a screw which also rotates. The centrifuge also has a distributor preferably constructed as a tube for introducing the material to be centrifuged into the centrifuging chamber. The distributor is oriented in an angular manner, particularly perpendicularly, with respect to the center axis of the screw, the material to be centrifuged being guided through an axially extending inflow tube into the distributor.
In the case of solid bowl screw centrifuges, the material to be centrifuged is to be accelerated to the circumferential speed of the screw at the diameter of the liquid level (surface) in the screw channel. The relative velocity at the entry into the centrifuging chamber of the liquid surface is to be as low as possible.
As a result of the acceleration to the circumferential speed of the screw at the liquid level diameter on the driving walls of the distributor, a surface flow is created in the distributor whose velocity increases considerably with the radius, specifically to a value which is approximately equal to the circumferential speed of the screw at the liquid level diameter.
From U.S. Patent Document U.S. Pat. No. 5,403,486, it is known to provide the area of the feeding of material to be centrifuged, in the widest sense of the word, the distributor, of a solid bowl screw centrifuge with a larger number of outlet openings which are aligned at various angles with respect to one another. However, this requires relatively high expenditures and, in addition, no lowering of the relative velocity is achieved.
From German Patent Document DE 1 293 089, it is known to cover nozzle-type distributor openings in the centrifuging chamber with a baffle plate which deflects the material to be centrifuged in order to reduce flows. However, this measure is not sufficient for an effective reduction of swirls.
The invention develops the solid bowl screw centrifuge of the above-mentioned type such that the relative velocity of the material to be centrifuged is reduced in a constructively simple manner when entering the liquid surface.
The present invention is a solid bowl screw centrifuge comprising a centrifuging chamber having a rotatable screw with a center axis and a rotatable drum surrounding the centrifuging chamber. It also includes an axially extending inflow tube for guiding material to be centrifuged into a distributor, the distributor being oriented in a substantially perpendicular manner with respect to the center axis of the screw and configured for introducing the material to be centrifuged into the centrifuging chamber. The distributor further includes at least one wall having a surface structure that includes projections configured such that a substantial portion of the material to be centrifuged flowing through the distributor must flow around at least one of the projections on an essentially radial path that extends in a direction of a centrifugal force such that the projections exercise a braking effect which counteracts an acceleration of the material to be centrifuged. The distributor may also or alternatively include at least one wall having a step-shaped surface structure extending in a circumferential direction.
According to another embodiment, at least one wall of the distributor is provided with a surface structure consisting of at least two or more radially mutually offset rows of projections. The projections of the rows are axially offset with respect to one another such that essentially no radial free flow channels are formed on the wall.
The embodiments of the present invention provide for an effective and nevertheless simple and relatively inexpensive manner such that at least the essential portion of the material to be centrifuged, but preferably the entire material to be centrifuged, can no longer flow in a direct radial path out of the inflow tube into the centrifugal chamber. Here, the word “radial” applies to the direction on the distributor wall in which the material to be centrifuged will essentially flow into the centrifuging chamber during the rotation of the distributor as a result of the centrifugal force. The term “radial” may also comprise an axial movement component and/or a circumferential component. It is important that at least the essential portion of the material to be centrifuged does not flow directly “in the direction of the centrifugal force” into the centrifuging chamber.
Although it is known from German Patent Document DE PS 1 272 231 to construct several grinding or crushing bodies on the distributor wall, direct paths radially into a centrifuging chamber still exist between these bodies so that a liquid is essentially not braked but enters the centrifuging chamber at an unchanged high velocity. The possibility of a benefit of projections for reducing the relative velocity of the material to be centrifuged when entering into liquid surface in a constructively simple manner was not recognized here.
According to another embodiment of the present invention, the projections are constructed as circular, rhombic or other n-cornered knobs.
In another embodiment of the present invention, the projections have a meander shape.
According to another embodiment of the present invention, at least one wall of the distributor is provided with a step-type surface structure which extends in the circumferential direction and which also causes a braking, among other things, as a result of swirls.
For all the embodiments of the present invention, the projections may be constructed as metal plates.
These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.